This invention relates in general to the sealing of containers and more particularly to a machine and process for installing inserts in container lids.
One of the most effective ways to seal a container, particularly a food container having a large mouth, is to interpose a foil seal between the mouth of the container and the lid which fits over that mouth. Preferably, the metal foil is attached directly to the mouth of the container independently of the lid so that even if the lid is removed, the contents of the container are still protected from contamination. The lid, of course, may serve as a closure after the foil has been broken to gain access to the contents in the container. Plastic containers lend themselves quite well to this type of sealing arrangement, since their rims when heated become pliant and tacky. The heated container rims thus adhere to the foil seal, and at the same time conform to any irregularities in it. Furthermore, by induction heating the foil, the heat necessary for effecting the seal may be localized so as not to damage the remainder of the container or harm its contents.
U.S. Pat. No. 4,095,390 discloses a machine and process for rapidly heat sealing foil disks to the mouths of plastic containers on an assembly line basis. However, the machine and process function best when the foil disks are retained in the lids as the lids are installed on the containers. In other words, it is desirable to place the lid and foil disk on the container as a unit and then heat seal the foil to the container mouth, instead of first placing the seal disk over the container mouth, then perhaps heat sealing, and finally installing the lid. Indeed, the lid serves to protect the foil disk as the disk and lid are handled. The lid further holds the foil disk flat as it is placed on the container mouth and guides the foil disk into a concentric disposition with respect to the mouth. Even so, wrinkles and other irregularities sometimes occur in the foil disk at the location where the plastic container mouth adheres to it, and these irregularities can produce a defective or incomplete seal.